There is increasing interest in wireless data communications, such as mobile computing, wireless messaging, facsimile, file transfer, and database access. Together with the trend of untethering computers from the desktop and the desire for universal connectivity, packetized cellular communications is becoming more and more important, and is being considered as the third generation of wireless networks.
Typical cellular networks are comprised of a large number of base stations. Each base station has an assigned coverage area (i.e. cell). In order for a mobile terminal to initiate a call, the cellular phone of the mobile is powered on and it scans the frequencies of a group of control channels for the strongest reception available. Once the appropriate control channel has been selected there is an exchange of messages between the base station and the mobile phone wherein the called terminal number is forwarded to the base station and a transmission channel is allocated to the mobile phone.
Undesirably, such a procedure requires that the mobile handset has the capability to: (1) scan a band of frequencies, (2) make power measurements, and (3) transmit the power measurements to the base station. Substantial functionality in the handset is required. Accordingly, there is a need for a technique that minimizes such processing to increase the efficiency of the mobile terminal.
Additionally, during an active communication, a mobile terminal that is leaving the coverage area of one base station must be "handed-off" to the next base station, whose coverage is the one the mobile is entering. In existing circuit switched systems this hand-off process is done via continuous communications between the base station and the mobile. Such a technique has its own system-level switching and control capability--a higher layer in the mobile network, operating above the individual cells. Through continuous, real-time measurements and comparisons of the signal strength received from the individual base stations, the mobile may initiate the handing-off of its call in progress to another cell. Such switching of a call is done "on-the-fly" without dropping or disrupting the call in progress. In general, substantial overlap in coverage areas between adjacent cells is required to insure high quality reception during hand-offs.
Unfortunately, such a hand-off technique may not be effective in a packet switched wireless system, due to the intermittent or bursty nature of the data traffic. Accordingly, there is a need for an effective hand-off procedure for use in packet switched wireless systems.
Additionally, future mobile platforms may be battery power and computation power limited. Thus, simpler procedures that reduce the amount of processing by the mobile platform may be required.